RE: Turbo Boost Noises (200Q)

[Ed Kellock <EKELLOCK@ECS-INC.com>]

	Could it be drivetrain noise?  It is a these times of high boost
that the drivetrain is most stressed and if engine and/or trans mounts
are not up to par, there could be a unique occurrence of noise related
the drivetrain, especially during an extreme transition from high stress
to low stress.  I believe there is a CV joint on each end of the center
driveshaft and a Ujoint in the middle.  One of these could be
momentarily touching something generating the rapid-fire thumping...

	(The phrase that generated this ideas was "a quick drumroll on
my floorboard with two rubber malletts".)

> -----Original Message-----
> From:	Michael Callaghan [SMTP:mikecallaghan@yahoo.com]
> Subject:	Turbo Boost Noises (200Q)
> 
> This may be related to another problem I've seen discussed here. If
> so, please forgive me. 
> 
> I have a noise (who doesn't?).
> 
> At first I thought it was something in the suspension. It seemed to
> happen only during shifts from a lower to a higher gear. It sounds
> like muffled machine-gun fire. Or, for the non-violent types, it
> sounds as though someone is doing a quick drumroll on my floorboard
> with two rubber malletts.
> 
> Anyway, I've narrowed it down to this: the sound only occurs AFTER any
> amount of turbo boost (1.0 or higher) on the boost gauge. It occurs
> only when the boost drops off quickly (e.g., I let off the gas to
> shift). If I ease off the gas pedal slowly and let the boost drop
> below 1.0, then shift, the noise does not appear.  
> 
> The sound apparently originates from the area near the ECU. I have not
> yet determined its exact location. 
> 
> Does anyone know where to check from here? Please don't tell me to buy
> the manuals. I'm working on that already (thanks).
> 
> MikeC
> '90 200Q
> '98 Expedition
>